Les Chevaliers de l’Ordre de la Terre Plate, Part I: Allègre and Courtillot

November 18th, 2007 by raypierre

Allègre claims that the disappearance of the glaciers on Kilimanjaro is due to moisture supply changes arising from tectonic uplift, and has nothing to do with global warming. This claim appeared over a year ago in Allègre’s column in L’Express, and was discussed in an earlier RealClimate post on Allègre. Essentially, Allègre failed to understand that the tectonic events referred to in the Science paper he cited affected the African climate millions of years ago, whereas the present Kilimanjaro glacier didn’t even come into existence until around 10,000 years ago. The erroneous claim about Kilimanjaro is repeated in Ma vérité sur la planète (p.120), despite ample time and opportunity to correct the mistake. So much for vérité ("his" or otherwise).

Allègre says that "common sense" casts doubt on the idea that CO2 could have such a controlling effect on climate, because its concentration is only 300 parts per million (p.104). This "common sense" flies in the face of over a century of meticulous physics going back to the time of Tyndall, which shows precisely why certain trace gases have such a strong influence on infrared absorption by the Earth’s atmosphere.

Allègre says we "know nothing" (p.109) about the Dansgaard-Oeschger events and other form of millennial variability appearing in the ice-core record. From this statement, I think you are supposed to infer that since we "know nothing" about the events it could well be that the current warming is just the latest warm phase of such a thing. To be sure, there’s a great deal still to be learned about millennial variability, but the phenomenon has been the subject of several hundred peer-reviewed scientific papers, dozens of conferences, and a major study by the US National Academy of Sciences. We know enough about the pattern of such events and the mechanisms involved to essentially rule out the possibility that the recent warming is a related form of natural variability. We also know enough to worry about the possibility that climate change due to greenhouse gas increases could trigger massive ocean circulation shifts of the sort that were involved in past millennial variability.

Allègre says that under an increase of CO2 there would be no warming at the equator, whereas the predicted warming at the equator is in fact only somewhat below the global mean warming. He states correctly that the warming is strongest at the poles, but states without support that a 10ºC warming would be no big deal (p.122). This is quite a startling statement, given that a much more moderate warming has already caused substantial loss of Arctic sea ice. Part of his misconception may come from the fact that he thinks that the temperatures at "the poles" range from "-30 to -60ºC." (p.122) If that were really true, there would be no open water in the Arctic at the time of the sea ice minimum. It is easily verified that this is not the case, and indeed the Arctic commonly gets up to 0ºC in the summer, and sometimes more.

Ignoring the numerous independent studies of the instrumental record of the past century, he says the Phil Jones analysis of this data has been "put seriously in doubt" (p.100). And by what means? A comparison of Jones’ global mean data with an unpublished analysis of the average of a limited number of hand-picked European stations — presented as the epitome of the Geophysicists’ incomparable expertise at time-series analysis! More on this when we come to discuss Courtillot.

Helpfully, Allègre advises modellers that "It is necessary to avoid basing predictions of future climate on a global mean whose status is vague." (p.106) Evidently he is unaware that general circulation models have been simulating geographical variations of future wind and temperature changes at least since the 1970’s, and that maps of such changes have been included in every IPCC report going back to the very first. Oh, but I forget. Elsewhere Allègre states that "nobody reads" the IPCC reports (p.115). Evidently, this statement applies to at least one person.

Continuing his display of ignorance of the modelling enterprise, Allègre wonders why modellers put CO2 in their models, and concludes that it is only because they happen to know how it has varied over the centuries. Could a century of meticulous laboratory and field work documenting the radiative effect of CO2 perhaps have something to do with modellers’ preoccupation with this gas? Evidently not in Allègre’s universe. But there’s more: "Because one doesn’t well understand how clouds form, one neglects them! Because one has not mastered the role of aerosols and dust, one neglects them!" (p.104) This is not at all true. Clouds, aerosols and dust (as well as solar irradiance variations and volcanic eruptions) are all included in modern models. Models that leave out the influence of the CO2 rise fail to reproduce the warming of the past 30 years, and it is precisely for this reason that CO2 is confirmed as the prime culprit in global warming.

Allègre makes a number of false or misleading statements concerning the contents of the IPCC Fourth Assessment report. He claims that this report (contrary to French media coverage) "considerably toned down" its conclusions compared to previous reports (p.119). By way of evidence, Allègre states "For a doubling of CO2 emissions the temperature of the globe will rise between 2 and 4.5ºC in a century. The previous report said between 1.5 and 6ºC." (p.119) First of all, the IPCC statements on climate sensitivity refer to a doubling of CO2concentration, not CO2emissions, but let’s give Allègre the benefit of the doubt and assume this is just another instance of sloppy writing rather than true misunderstanding. Even so, Allègre is mixing up his apples with his pommes de terre in this statement. Though the climate sensitivity range narrowed from 1.5-4.5ºC previously to 2-4.5ºC now, reducing the likelihood of low climate sensitivity, the range of predictions for 2100 remain largely unchanged (and are moreover not strictly comparable between the reports given changes in the way "likelihood" is estimated). In a similar vein, Allègre claims that the IPCC reduced its forecast of sea level rise, which is not the case.

And there’s more. He says that IPCC has "modified, though not completely abandoned, its argument concerning 20th century temperature rise." (p.119) This evidently refers to Allègre’s belief that one of IPCC’s main arguments has been that CO2 must be responsible for temperature rise because (ben voilà!) they both go up! It’s hard for IPCC to abandon an argument it never made, and in any event the Fourth Assessment Report probably devotes more space to discussing the twentieth century temperature record, using more techniques, than any earlier report. And yes it does (pan to shot of Galileo here, speaking through clenched teeth as he bows before the inquisition) still go up (and by essentially the same amount as previously estimated). Continuing the theme of abandonment, Allègre says that the IPCC has "abandoned" its argument regarding the implications of ice-core CO2 and temperature variations. Actually, not. There is no change in the way IPCC interpreted the Vostok isotope and CO2 curve, which appears both in the 2001 and 2007 reports (the latter with Epica extensions into earlier times). The discussion appears in Chapter 6 of the Fourth Assessment Report (p 444 fig 6.3), but how could Allègre be expected to know that? Nobody reads the IPCC reports, right?